Spray guns are widely used to apply a liquid to a substrate in a variety of industries. In the known spray guns, the liquid is contained in a reservoir attached to the gun from where it is fed to a spray nozzle. On emerging from the spray nozzle, the liquid is atomised and forms a spray with compressed air supplied to the nozzle. The liquid may be gravity fed or suction fed or, more recently, pressure fed by an air bleed from the compressed air line to the reservoir or even from the spray gun itself.
A common application of spray guns is in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. A typical paint finish may require application of a primer, base coat, top coat and a clear lacquer. Traditionally, the reservoir is a rigid pot detachably mounted on the spray gun by engagement of complementary screw threads on the spray gun and pot. The spray gun and pot have to be thoroughly cleaned when changing the liquid to be sprayed to avoid cross-contamination which may adversely affect the finish. This is especially important when spraying part of a vehicle to match exactly the colour of the existing colour of the adjacent bodywork. Cleaning the spray gun and pot is time consuming and often requires the use of solvents which are costly and may present a health hazard to the operator.
We have previously proposed in WO 98/32539 a reservoir in which the liquid is contained in a disposable lid/liner assembly. The liner is in the form of an open-topped container that is a close fit inside an outer rigid pot, and the lid is secured over the open end of the liner by a collar screwed onto the pot. The reservoir is releasably connected to the spray gun by means of a spout integral with the lid and through which liquid is withdrawn from the reservoir in use.
In this way, after spraying, the reservoir can be detached from the spray gun, the collar released and the lid/liner assembly removed from the outer pot and thrown away. The outer pot and collar can then be re-used with a new, clean liner and lid for supplying a different liquid to the spray gun. As a result, the amount of cleaning required is considerably reduced and the spray gun can be readily adapted to apply different liquids in a simple manner.
For some applications of the spray gun, a larger volume of liquid than the reservoir can hold may be required. For example, when painting a large area or applying several coats of the same liquid to the same or different vehicles such as when using a primer or lacquer finish. In this case, the reservoir can be detached from the gun, the collar released and the lid removed to allow liquid to be added to the liner. The reservoir is then re-assembled and re-attached to the spray gun.
Dis-assembly and re-assembly of the reservoir is time consuming and can result in spillage of liquid especially when the lid is removed from the liner. Also, removing the lid to add more liquid to the liner increases the risk of contamination from other sources, e.g. dust or dirt.
The alternative of adding liquid to the reservoir through the spout in the lid so as to avoid dis-assembly is slow due to the spout being of small size compatible with the connection to the spray gun so that liquid cannot be freely poured into the reservoir through the spout. Also the spout may contain a filter or a filter may be positioned in the lid across the inner end of the spout to remove any unwanted solid particles contained in the liquid withdrawn from the reservoir in use. Access to the filter requires dis-assembly of the reservoir and the presence of such filter further slows the addition of liquid to the reservoir through the spout.
Furthermore, if the liquid contains solid particles these will be trapped on the wrong side of the filter. As a result, when the reservoir is re-attached to the spray gun, the particles may be picked up with liquid withdrawn from the reservoir and pass to the spray gun. This may lead to a blockage within the spray gun. Alternatively or additionally, the particles may be applied with the liquid to the surface being sprayed with the result that the surface may have to be re-sprayed.